Fuel cells are efficient clean power generation systems, and in recent years, the fuel cells have been paid attention as novel energy systems for automobiles and home uses. For cell sealing members for the fuel cells, low-cost materials excellent in heat resistance, acid resistance, resistance to permeation of gases and high-speed moldability are desired, and in the existing circumstances, a fluororubber is applied from the viewpoints of heat resistance and acid resistance, a butyl rubber is applied from the viewpoint of resistance to permeation of gases, and a silicone rubber is applied from the viewpoints of heat resistance and moldability. To meet the requirement of high-speed moldability, however, usual materials are insufficient, and in this case, a method in which a liquid silicone rubber is used and LIM (liquid injection molding) is applied has been considered.
Although the silicone rubber is excellent in heat resistance and high-speed moldability, it is inferior in acid resistance and resistance to permeation of gases, and the power generation performance of the existing fuel cells is low. Therefore, studies of improvements in the power generation performance have been promoted. As the power generation performance is enhanced in future, the reaction temperature in the cell or the like tends to become higher. On that account, performance at higher temperatures is required also for the sealing materials.
Then, a rubber composition that has solved the above problems, i.e., problems of moldability and heat resistance, has been developed. This rubber composition is excellent in high-speed molding and is favorably used for fuel cell sealing members having excellent heat resistance, acid resistance and resistance to permeation of gases (patent document 3). However, specific fuel cell sealing members sometimes exhibit insufficient mechanical properties.
As the electronic equipment manufactured articles are downsized and the performance thereof is enhanced, making their component parts smaller and thinner is required. However, if the component parts are made smaller, assembly workability in the manufacturing is deteriorated. Therefore, uniting or combining various parts in one is required. In the case of a gasket for a hard disc drive that is an electronic memory device, for example, a method in which a single rubber or a foamed urethane sheet is interposed by a metal cover, such as a stainless steel cover or an aluminum cover, and they are bonded with an adhesive to unite them in one has been proposed (patent document 1).
However, if the gasket has high hardness (counterforce) in the adoption of the above uniting method, a problem of deformation of the metal cover occurs because the metal cover has been made lightweight and thin.
Then, a styrene-based thermoplastic elastomer has been disclosed as a gasket material (patent document 2). It is described that because the styrene-based thermoplastic elastomer has low hardness and needs no vulcanizing step differently from the rubber materials, simplification of the production process and recycling are possible.
However, because of generation of heat due to enhancement of performance (high rotational speed) of the hard disc drive and because of adoption of such a material in automobiles, the material tends to be exposed to higher temperatures (particularly not lower than 80° C.) in the use environment. In such environment, the conventional styrene-based thermoplastic elastomer suffers a problem of permanent set at high temperatures that is one of mechanical properties, and there is limitation on the performance.
Electric wire connectors serve to connect and branch electric wires, and comprise a pair of male and female resin frames capable of being connected through one-touch operation, an electric wire and a sealing member. The sealing member is mainly used as a dust seal between the electric wire and the resin frame. For the electric wire connector sealing member applied to use of this kind, sealing properties against thin electric wires and insertion properties are required, and in the past, a silicone rubber and a nitrile rubber, which are of low hardness and oil-bleeding type, have been employed.
These rubbers, however, mainly contain a silicone oil as a plasticizer and therefore have a problem that the plasticizer adheres to electric contact points during the use to cause insulation at the electric contact points and thereby bring about troubles in the flow of electric current.
Then, a rubber composition that has solved the above problem has been developed and favorably used for electric wire connector sealing members (patent document 3).
However, a requirement of enhancing mechanical properties for the electric wire connectors has been also increased. In the case of the conventional sealing members, the crosslinking rate after vacuum defoaming is sometimes lowered, and in addition, mechanical properties are insufficient. Therefore, improvement of properties has been desired.
Patent document 1: Japanese Patent No. 2517797
Patent document 2: Japanese Patent No. 2961068
Patent document 3: International Publication WO 03/057777